The present invention relates to printing high quality continuous tone images by microfluidic pumping of colored inks onto receivers.
Microfluidic pumping and dispensing of liquid chemical reagents is the subject of three U.S. Pat. Nos. 5,585,069, 5,593,838, and 5,603,351, all assigned to the David Sarnoff Research Center, Inc. The system uses an array of micron sized reservoirs, with connecting microchannels and reaction cells etched into a substrate. Electrokinetic pumps comprising electrically activated electrodes within the capillary microchannels provide the propulsive forces to move the liquid reagents within the system. The electrokinetic pump, which is also known as an electroosmotic pump, has been disclosed by Dasgupta et al., see xe2x80x9cElectroosmosis: A Reliable Fluid Propulsion System for Flow Injection Analysesxe2x80x9d, Anal. Chem. 66, pp 1792-1798 (1994). The chemical reagent solutions are pumped from a reservoir, mixed in controlled amounts, and them pumped into a bottom array of reaction cells. The array may be decoupled from the assembly and removed for incubation or analysis. When used as a printing device, the chemical reagent solutions are replaced by dispersions of cyan, magenta, and yellow pigment, and the array of reaction cells may be considered a viewable display of picture elements, or pixels, comprising mixtures of pigments having the hue of the pixel in the original scene. When contacted with paper, the capillary force of the paper fibers pulls the dye from the cells and holds it in the paper, thus producing a paper print, or reproduction, of the original scene. One problem with this kind of printer is the tendency of the ink to dry out and plug the small openings which deliver the ink to the paper. Another problem is that of controlling the density of the print. The force of capillary attraction can pull more ink than is needed from the printing apparatus, leading to excessive density in the print, as well as color bleeding and incorrect colors.
It would be desirable to have a compact, low powered printer which uses an ink that is highly effective in microfluidic printing and overcomes the above problems.
An object of this invention is to provide an rapid way to print a high quality continuous tone image.
It is another object of this invention is to provide improved ink which can be used in microfluidic printing and which does not dry out and plug in the printer and is highly effective for being fixed to a receiver.
These objects are achieved by a method for microfluidic printing comprising:
a) pumping and mixing colored inks which comprise a mixture of colorants, fluids, and gel-forming or gel-initiating ingredients to form ink pixels and to transfer such ink pixels to a receiver transferring position; and
b) transferring the ink pixels to a reflective receiver which contains gel-forming or gel-initiating ingredients so that the ingredients in the transferred ink pixels and in the receiver react to form a gel and the viscosity of the transferred ink rapidly increases to limit the flow of ink pixels whereby such ink pixels are fixed to the receiver and overprinting of colors is minimized.
The present invention provides high quality microfluidic prints by using an ink which does not clog or plug through the effective use of gel-forming ingredients and gel-initiating ingredients and permits the ink pixels to be readily fixed to a receiver. As the ink pixels are transferred, the viscosity of the ink rapidly increases, limiting ink flow and preventing color bleeding. The increasing viscosity prevents the printing of overly dense colored pixels. The prevention of overly dense colored pixels provides for improved image quality. The use of inks in accordance with the present invention does not effect the power requirements of the printer and permits fast printing since all the pixels are printed simultaneously.
Another feature of the invention is that the printer may be operated under a wide variety of conditions and temperatures without color bleeding and excess print density.